NPR has a very good 5 minute program produced in 2008 on the 40th anniversary of President Johnson’s stunning announcement that he would not seek another term in office. As NPR producer John McDonough observed, “nobody saw it coming.” You can learn more about it, and also hear the president make his historic statement here. You can also read the entire text of the speech here, in which President Johnson begins by proclaiming his intention to wind down the Vietnam War.